The present invention is directed to an apparatus configured for use with a door or other barrier for maintaining the door or other barrier in a position and capable of resisting a trans-barrier force less than a predetermined magnitude. When the trans-barrier force exceeds the predetermined magnitude, the apparatus is designed to yield and allow the barrier to move in response to the trans-barrier force, thereby avoiding damage to the barrier and, further, avoiding damage to adjacent supporting structures for the barrier, such as guide rails, supports, tensioning mechanisms, and the like.
The preferred embodiment of the present invention is particularly adaptable for use with a door of the roll-up type which is generally used for environmental control between two spaces, such as between sections of a warehouse, or the like. In such doors, a motor-driven roller controls the upward and downward movement of the door to control access through an opening. An assembly of cables, associated pulleys, and tension springs serves as a tensioning mechanism. The tensioning mechanism is driven by the roller motor and connected to a guide follower apparatus. The guide follower apparatus is attached to the bottom, or leading edge, of the roller door and interacts with guide rails adjacent the opening. In such installations, the door is generally flexible and is kept under tension to aid in maintaining alignment of the door with respect to the guide rails and the opening.
It is common that such door installations are subjected to abuse during normal operations by the impact of machinery, such as fork lifts, with the bottom (leading edge) of the door. In previous designs, such abuse inflicted serious damage to the door and its associated guide rails, tensioning mechanism, and other parts. Such damage often jammed the door in its down (closed) position, causing serious delays in operations in spaces about the door since the door blocked access through the opening.
Previous efforts have been made to accommodate these destructive forces accidentally imparted to such doors. One solution has been to provide a hinged guide rail so that application of force to the door causes the hinged panel of the guide rail to pop loose and rotate away from the guide follower attached to the bottom, leading edge, of the door. That swinging open of the guide rail allowed the door and guide follower to swing free in response to the application of the destructive force.
The hinged guide rail solution had problems and shortcomings: the cables in the door tensioning mechanism could snarl, stretch, break, or otherwise become damaged; associated pulleys and tension springs of the tensioning mechanism could similarly be damaged; and, perhaps most important, since the guide rails were generally placed adjacent the opening, as opposed to within the opening, the hinged guide rail only accommodated trans-barrier forces in one direction, away from the wall surrounding the opening. Trans-barrier forces applied in the opposite direction (toward the wall) would not operate to pop open the hinged panel of the guide rail and would serve only to drive the door and its associated guide follower against the wall surrounding the opening. Of course, driving the door against the wall caused damage to the guide follower, door, guide rail, tensioning apparatus, and other parts of the door installation.
The present invention is designed to overcome the shortcomings of these previous attempts to provide a trans-barrier force accommodation mechanism to avoid damage to a barrier and its associated structures and mechanisms. In one of its embodiments, the present invention uses a structure which accommodates trans-barrier forces in two directions.
Further, great precision of determination of the predetermined magnitude of the trans-barrier force at which the apparatus will allow the door to yield can be achieved in the present invention through the use of a shear pin-type or similar assembly.